A carbon nanotube (CNT) is a one-carbon-atom-thick layer of graphite (i.e., a graphene sheet) rolled into a seamless, closed cylinder. Typical CNT diameters are a few nanometers (nm) or less but they can have lengths that are in the millimeter range or larger.
Carbon nanotubes exhibit unique physical, electrical, and chemical properties that offer the potential for revolutionary impact in a broad range of diverse applications areas, such as electronics, materials, medicine, law enforcement, architecture, national defense, and fashion. These properties depend on the physical characteristics of the carbon nanotube, such as the number of walls (i.e., single-wall, double-wall, etc.), diameter, and chirality (i.e., the way the graphene sheet is wrapped about itself). For example, depending upon its structure, a CNT can behave like a metal, such as gold or aluminum, or like a semiconductor, such as silicon or gallium arsenide.
Carbon nanotubes are synthesized in a number of ways, including arc discharge formation, laser ablation, and chemical vapor deposition. Unfortunately, it has proven difficult to selectively produce large volumes of CNTs having uniform material characteristics in a cost-effective manner. This has proven to be a barrier to their use in many applications—particularly those wherein a specific chirality is desired.
In order to isolate particular types of CNTs, high-volume, non-selective synthesis has been coupled with post-synthesis sorting techniques. Several sorting approaches have been demonstrated, the most promising of which is based on density-based centrifugation of a slurry of disparate carbon nanotubes. This approach is still too expensive for consideration in large-scale systems, however.
A method for synthesizing carbon nanotubes having improved purity would represent a significant advance in the state-of-the-art in nanotechnology.